NASHVILLE — President Trump is planning to focus his midterm campaigning this summer on red states with competitive Senate races where he has a deep reservoir of support and can bring a message devised to stoke partisan outrage.

The strategy is intended to take advantage of his star power among core Republican supporters while minimizing his exposure in states with competitive congressional races where his polarizing presence could help motivate Democrats as well as independents and moderate Republicans.

Mr. Trump’s appearance Tuesday in Nashville was an example of how he plans, for now, to campaign where he can have an immediate effect because of his ability to either fund-raise or draw local news media attention, according to White House officials who described the strategy on the condition of anonymity because they were not authorized to discuss it.

After a day in Washington, he flew to Tennessee to attend a fund-raiser and rally for Representative Marsha Blackburn, a Republican running for the seat being vacated by Senator Bob Corker, who is retiring. Ms. Blackburn has embraced Mr. Trump tightly in her bid in a state he won with more than 60 percent of the vote in 2016, and on Tuesday evening, crowds lined up in the streets around the old Nashville Municipal Auditorium, many wearing plastic slickers against pouring rain, to catch a glimpse of the president.

Ms. Blackburn’s Democratic opponent is expected to be Phil Bredesen, a former Tennessee governor, after the state’s primaries in August.

In the coming weeks, the strategy will also take Mr. Trump to North Dakota, Montana, Missouri, Indiana and West Virginia — all deeply red states he won handily in 2016 with endangered Democratic senators. It does not include immediate plans to go to Florida, Michigan, Nevada or Ohio, although those states could be added to the president’s itinerary as the November contests draw closer, the officials said, and his schedule is likely to fill out with well over a dozen stops each month.

White House officials, who have pushed to keep Mr. Trump from getting involved in primary races, said that the focus on the six red states before primaries have taken place will give him a chance to bloody the Democrats there while Republicans are still settling on their nominees.

On Tuesday morning, Mr. Trump previewed a combative political message, charging that the special counsel investigating Russia’s interference in the 2016 presidential elections — and whether his campaign played any role — was a Democratic-run scheme to steal the 2018 congressional contests.

“The 13 Angry Democrats (plus people who worked 8 years for Obama) working on the rigged Russia Witch Hunt, will be MEDDLING with the mid-term elections, especially now that Republicans (stay tough!) are taking the lead in Polls,” Mr. Trump tweeted.

With Republicans holding just a one-seat majority in the Senate, their most urgent priority this summer is to soften up the red-state Democratic senators or candidates who have been trying to straddle the demands of their anti-Trump base without offending the Trump-friendly electorates in their state.

And in many of these races, the Republican has not yet been selected, was recently nominated or, as with Ms. Blackburn, is still not well known in every corner of the state. So party officials view Mr. Trump as the logical messenger to both unify the Republican base behind their standard-bearer and take aim at the Democrat.

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Trump supporters in Elkhart, Ind., this month. “Only he can fill these arenas with the folks wearing the MAGA hats and T-shirts, and the Republican candidates need to capture some of that intensity,” a Republican strategist said.CreditDoug Mills/The New York Times

But it is the second of these tasks where he is seen to be most useful. In both his own campaign and a series of special elections since, Mr. Trump has been far better equipped to knock down a rival than to lift up an ally. The hope now is that his savage attacks, penchant for mimicry and resourcefulness in nickname creation — recall “Lyin’ Ted” and “Little Marco” — can be turned to devastating effect on the very Senate Democrats who have gone to lengths to avoid publicly breaking with him.

“He’s the definer in chief,” said Rob Collins, who ran the National Republican Senatorial Committee when the party took back the chamber in 2014. “He comes in, defines the opponent in a way that’s unconventional and unorthodox, but it sticks.”

Few are more delighted about Mr. Trump’s summer tour than Senator Mitch McConnell of Kentucky, the majority leader, and his lieutenants.

“He can strip bark more than anybody I’ve seen,” Josh Holmes, a top adviser to Mr. McConnell, said of Mr. Trump. “And the bang for your buck you get out of these visits is like 10 to 1 what any other president can do. Imagine the local news station doing something else for the first 15 minutes of the broadcast if Trump is in town.”

The hope among Republicans is that the president’s attacks are not just a one-night-only affair, but that his framing can be picked up by their nominee and other surrogates and, if it holds, eventually be deployed in paid advertising.

That is certainly the hope in Indiana, where Mr. Trump held a rally shortly after the Republican primary this month and immediately bestowed a nickname on Senator Joe Donnelly, an affable but little-known first-term Democrat: “Sleepin’ Joe.” At an event that White House officials view as a model, the president ridiculed Mr. Donnelly while also leveling the more conventional charge that the senator would “do whatever Chuck Schumer and Nancy Pelosi tell him to do,” naming the Democratic Senate and House leaders.

To Republicans in these red states, the president’s trips are crucial building blocks to avoiding the fate that befell Obama-era Democrats, who suffered deep midterm losses because they could not rouse sympathetic voters to cast ballots when the president was not on the ballot.

“There’s a whole bunch of people who voted for the president who the party structure isn’t going to motivate to turn out or stay involved,” said Anne Hathaway, a strategist and former top Republican National Committee official. “He winds them up and gets them engaged.”

Describing Mr. Trump’s high-decibel rallies as something akin to a summer rock tour, Ms. Hathaway said, “Only he can fill these arenas with the folks wearing the MAGA hats and T-shirts, and the Republican candidates need to capture some of that intensity.”

The president, however, is notably not in demand in many of the districts with the most competitive House races, because the party’s challenge in those races is not defeating Democrats on Trump-friendly turf but protecting their own incumbents in districts where the president is seen as a divisive figure.

And privately, even some pro-Trump Republicans view the red-state tour as the safest approach for a politician more apt to mock a teleprompter than to faithfully adhere to it. Headlining summer events in states he won handily is a way to rally the party base without provoking the sort of campaign-altering chaos he could incite closer to the election.

Aides to Mr. Trump said that officials have focused heavily on the right-track, wrong-track numbers in polling to guide them on the climate nationally, which they believe has improved. And they said that Mr. Trump is still a positive influence in several House races in districts he carried in 2016, and that he is expected to campaign in some in the fall.

Mr. Trump’s schedule could ultimately include stops in Ohio and Michigan, two states that the White House political director, Bill Stepien, keeps on one of the white boards in his office, one White House official said. And it is possible that in Florida, where Gov. Rick Scott is running for the Senate and Mr. Trump at this point could pose a problem, the president might get more engaged in the fall, when the season at his club in Palm Beach, Mar-a-Lago, reopens, and he has a place he knows to spend the night.

Julie Hirschfeld Davis reported from Nashville, Maggie Haberman from New York and Jonathan Martin from Washington.

A version of this article appears in print on , on Page A17 of the New York edition with the headline: A Combative March Through Conservative States to Attack Democrats. Order Reprints | Today’s Paper | Subscribe